1. Technical Field
The present invention relates to a substrate for a semiconductor device, a semiconductor device that is provided with the substrate, and an electronic apparatus that is provided with the semiconductor device.
2. Related Art
A substrate that is used in a display device such as, for example, an electrophoretic display device that is driven in an active matrix scheme and includes a base substrate and a plurality of pixel-switching elements arranged over the base substrate is known as a type of a substrate for a semiconductor device. For example, a plurality of transistors each of which functions as the pixel-switching element is arranged over the base substrate. Such a substrate for a semiconductor device is sometimes called as an “active matrix substrate” or a “transistor array substrate”.
As an example of related art, a transistor that functions as a pixel-switching element and has the following layered structure over the base substrate of a transistor array substrate is disclosed in Japanese Patent No. 4275671. The transistor has two gates. The gates partially overlap the source and drain of the transistor. A floating pattern partially overlaps the gates. With such a structure, it is possible to prevent the leakage of a current at the transistor, that is, the generation of a leakage current at the transistor when the transistor is in its OFF state.
However, the structure disclosed in Japanese Patent No. 4275671 has a technical problem in that, since each transistor has two gates, it will be difficult to miniaturize the transistor. For this reason, it will be difficult to enhance the high-definition display capability of a display device such as an electrophoretic display device or the like. The structure disclosed in Japanese Patent No. 4275671 has another technical problem as explained below. Though each transistor has two gates, if it is looked at from another angle, such a structure is equivalent to mere serial connection of two transistors each of which has one gate. Though such a structure makes it possible to reduce the leakage current of the transistor, the ON current of the transistor (i.e., a current that flows in a channel region when a predetermined voltage that is not lower than a threshold value is applied to the gate electrodes) will also drop.